# Pyrolyzed Parylene Electrodes for Detection of Tryptophan, Tyrosine, and Gonadotropin-Releasing Hormone

## TL;DR

This paper introduces a new type of carbon electrode that detects brain chemicals more sensitively than traditional ones.

## Contribution

Pyrolyzed parylene-N microelectrodes (PPNMEs) offer higher sensitivity and faster detection for neurochemicals.

## Key findings

- PPNMEs showed four times higher signal amplitudes than carbon-fiber electrodes for detecting neurochemicals.
- PPNMEs enabled sensitive detection of GnRH in brain tissue slices, including spontaneous release.
- PPNMEs exhibited faster electron transfer and enhanced secondary oxidation peaks due to surface roughness.

## Abstract

Sensitive and selective detection of neurochemicals such
as neuropeptides
is critical for understanding brain signaling. While carbon-fiber
microelectrodes (CFMEs) are widely used for these measurements, alternative
electrode materials and fabrication techniques could improve sensitivity
and versatility. In this study, we investigate pyrolyzed parylene-N
microelectrodes (PPNMEs) as a promising platform for making thin-film
carbon electrodes for the detection of electroactive amino acids and
neuropeptides. We evaluated the performance of PPNMEs for the detection
of tryptophan (Trp), tyrosine (Tyr), and the neuropeptide gonadotropin-releasing
hormone (GnRH), which contains these electroactive residues. PPNMEs
demonstrated significantly greater sensitivity with fast-scan cyclic
voltammetry, with signal amplitudes approximately four times higher
than those observed with CFMEs. After normalization for surface area,
PPNMEs exhibited 3-, 5-, and 2.7-fold higher signals than CFMEs for
Trp, Tyr, and GnRH, respectively. Additionally, PPNMEs facilitated
faster electron transfer kinetics, as evidenced by reduced oxidation
potentials. There were enhanced signals for secondary oxidation peaks
at PPNMEs because the rougher surface can trap intermediates near
the surface, facilitating detection of downstream electrochemical
reactions. Scan rate analysis indicates more adsorption-controlled
detection, contributing to improved sensitivity. Importantly, PPNMEs
enabled sensitive detection of GnRH in brain tissue slices, including
both puffed-on applications and spontaneous endogenous GnRH release
in the median eminence. These results highlight the potential of PPNMEs
as a new class of carbon-based electrodes, offering a promising alternative
to CFMEs for high-sensitivity, low-potential detection of neurochemicals
in biological tissues.